--plasma themes because of their svg nature can
have a minimum padding under which they are not
drawn correctly. In such cases background shadows
overlap and background internal drawing overlaps
in the center. That property protects from
such case by introducing a minimum background
thickness at all cases. Good example of the issue
is observed in behaveAsPlasmaPanel(s) that are
floating and have very good round corners.
Michail Vourlakos